Notes:

I don't like that most notes apps don't let you access to your files, relying instead in cloud synching. One of the few that gives you full control is https://f-droid.org/en/packages/net.gsantner.markor/

It let you chose a folder where to save your notes and can manage many types of files (markdown, txt, todo, csv, etc)

I like saving my notes on my SD card, I created different folders to work as notebooks, so for example, I have a folder named "comments" where I edit my comments before posting, one for lists, one for lyrics of songs I like and I'm thinking about making one for cooking recipes.

Music:

https://f-droid.org/en/packages/com.poupa.vinylmusicplayer/
https://f-droid.org/en/packages/player.phonograph.plus

and https://f-droid.org/en/packages/ch.blinkenlights.android.vanilla

Are the best for offline experience. I really like vinyl's and phonograph's plus UI, simple, yet powerful. Both supports lyrics, metadata editing and at least vinyl can connect to the internet to grab artist picture and bio which can be displayed offline, I'm not sure if phonograph can since it's main focus is privacy and to work fully offline.

The issue i have with both is that they don't work properly on my Samsung tab, I think is the awful Samsung bloatware that makes them stop, and not make full use of all their features.

Vanilla UI isn't the best looking but it has many features when combined with the extensions. The best Foss metadata fetcher and editor. The problem the app have is that it isn't update frequently, and at the moment it has a problem with the notifications. There's already a PR opened in github, so hopefully this get fixed soon.

Keyboard

I'm currently using 2 keyboard apps https://github.com/Helium314/openboard as my main and https://f-droid.org/en/packages/rkr.simplekeyboard.inputmethod When I'm tire of the autocorrector changing what I write. I know I can disable it on openboard, but most of the times I actually use it and simple board is just more fluid.